1. Technical Field
The present invention relates to polyurethane (hereafter referred to as “PU”) foam plastic technology.
2. Description of the Related Art
Polyurethane foam is normally produced through the polymerization of isocyanates and hydroxyl compound group. Depending on its hardness, polyurethane foam can be classified as flexible and rigid, wherein flexible foams are the largest category of polyurethane foams. In general, PU foam has properties of great elasticity, high flexibility, very good tensile stretch and compressive strength; it's also chemically stable and exhibits resistance to most of solvents and oil base liquid. PU foam has a good abrasion resistance, which is 20-fold better than natural sponge. Additionally, PU foams are utilized in manufacturing children's toys because it shows desired characteristics such as easy processability, good athermancy and adhesivity as one of the excellent cushioning materials.
Present PU foam products exhibit several deficits in the process of playing: 1) the large amount of open pores prompt adsorption of moisture in contact, plus its slow-drying nature, causing the growth of mildew so as to harm children's health; 2) Stains from a muddy damp environment cannot be thoroughly cleaned; 3) the flexible cover of the product is easily damaged while playing.
A Chinese Patent CN1247124 published on 2000 Mar. 15, entitled as “A method of manufacturing PU foam seamless leather pads”, disclosed a manufacturing method of seamless leather pads. The invention involves processes of putting the polyurethane PVC or PU leather onto the pre-shaped negative mold, and then vacuuming to stretch the leather to tightly attach on the negative mold chamber with the negative pressure system of the vacuum suction device. A layer of PU with the thickness of 0.4-0.6 mm is formed on the inner surface of the leather. Then the liquid polyurethane material containing 30-40% of isocyanates and 60-70% of polyurethane is pumped into the mold chamber at high pressure. The product is obtained following completely foaming at 35-50° C. In the production, the successful binding between interior polyurethane and the exterior soft leather depends on the formation of polyurethane layer, which is 0.4-0.6 mm in thickness, on the inner surface of the soft leather. Additionally, this technique uses soft leather as outside cover. Soft leather, as a coil material of broad width offering solely simple and limited surface patterns, is unable to provide a rich variety of patterns and colors.